Method for making integral containers having precisely parallel vertical walls



3,400,111 CISELY J. L. SCHWARTZ Sept. 3, 1968 METHOD FOR MAKING INTEGRAL CONTAINERS HAVING PRE PARALLEL VERTICAL WALLS Filed Oct. 18, 1963 4 Sheets-Sheet 1 INVENTOR. 4400a A. sax/m1:

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METHOD FOR MAKING INTEGRAL CONTAINERS HAVING PRECISELY PARALLEL VERTICAL WALLS 4 Sheets-Sheet 5 Filed Oct. 18, 1963 m a m4 ms w III A. W i a ww h WWI/M Sept. 3, 1968 J. L. SCHWARTZ 3,400,111

METHOD FOR MAKING INTEGRAL CONTAINERS HAVING PRECISELY PARALLEL VERTICAL WALLS Filed Oct. 18, 1963 4 Sheets-Sheet 4 United States Patent 3,400,111 METHOD FOR MAKING INTEGRAL CON- TAINERS HAVING PRECISELY PARAL- LEL VERTICAL WALLS Jacob L. Schwartz, Covina, Calif., assignor, by mesne assignments, to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Oct. 18, 1963, Ser. No. 317,355 2 Claims. (Cl. 264-89) The present invention relates to a method for making integral containers having precisely parallel vertical walls, from a formable material which is characterized by contraction as it cools.

Certain types of containers have traditionally been made with precisely parallel vertical walls. For example, the conventional wooden box is fabricated from a plurality of flat members which provide the bottom, side and end walls thereof, and which are fastened together with nails or other equivalent fastening means. The present invention is clearly distinguished from methods for making those types of containers, however, in that the present invention is restricted in its application to integral, or one-piece, containers. Such containers may be made of metal, for example, but. are more typically made from thermoplastic materials such as a polyolefin.

In the manufacture of integrally formed containers it has heretofore been the established practice to form such containers with upwardly and outwardly diverging side and end walls. One reason for that type of constructionhas been to permit the nesting of superimposed containers. A more important reason for that construction, however, has been the necessity of providing draft on the mold in the forming process; that is, the upward .divergence of the walls has been necessary in order to permit the completed container to be stripped from, the mold afterthe forming operation was completed.

When integrally formed containers have been designed for stackable support it has heretofore been necessary, because of the upwardly diverging wall structure as described above, to modify one or more of the walls by incorporating vertical convolutions or stacking posts therein. Accordingly the industry has witnessed a great many complex varieties ofcontainers all of which have been expensive to design and manufacture, particularly in terms of the initial cost of tooling.

A significant limitation which has heretofore existed in the manufacture of containers has been that, when otherwise-identical containers of diiferent vertical heights were to, be, manufactured, it has been necessary to provide a separate set of tooling-for each such container height. The manufacturer has therefore been obliged to keep a great many sets of tooling on hand, although only one or a fewsets of the tooling were in use at any given time. The resulting operational costs have been very high because of the initial cost of the various sets of tooling, the cost of storage space for keeping the sets of tooling not being used, and the time and expense of changing from one set of tooling to another in a particular manufacturing set-up each timethat the manufacturing run was to be changed to a container of a different height.

In the manufacture of containers designed for stackability it has been necessary to maintain close mechanical tolerances on the parts of the containers that are interengaged when in the stacking position. Some forming processes which might otherwise be acceptable for thermoplastic materials, forexample, have not been ac- 3,400',1 1 l Patented Sept. 3, 19(58 One type of integrally formed container which has been in wide usage for a number of years is provided with aligned pairs of vertical grooves on its interior walls, and is designed to slidably receive partitions inserted vertically into these pairs of grooves. It has been desired to provide stackability for this type of compartmentable container, but because of the presence of the grooves on the interior wall surfaces of the container it has heretofore been impossible to design a completely satisfactory stacking arrangement for this kind of container.

A primary object of the invention, therefore, is to provide a method of forming integral containers having precisely parallel vertical walls.

Another object of the present invention is to provide a method of manufacturing stackable containers which do not incorporate stacking posts or convolutions in any of the walls thereof.

An additional object of the invention is to provide a novel method for manufacturing compartmentable containers of the type having aligned pairs of vertical grooves formed in the interior wall surfaces thereof, but which are also securely stackable in superimposed relationship.

Yet another object of the invention is to provide a manufacturing method which are peculiarly adapted to the economical manufacture of integrally formed containers having precisely parallel walls, from a polyolefin material.

The present invention is illustrated and described herein as applied to the forming of containers of the type disclosed and claimed in copending application Ser. No. 266,000, filed Mar. 18, 1963, now Patent No. 3,172,562. It will be understood, however, that the present invention is by no means limited to the forming of the specific type of containers disclosed in that copending application.

The objects and advantages of the invention will become more fully apparent from the following description considered in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a perspective view of a set of tooling provided in accordance with the present invention, and a sheet of thermoplastic material from which a container is to be formed;

FIGURE 2 is an elevational view, partially in crosssection, of the apparatus of FIGURE 1 as the forming operation is being commenced;

FIGURE 3 is a vertical cross-sectional view of the apparatus of FIGURE 1 as the forming operation is advanced to a later stage;

FIGURE 4 is a vertical cross-sectional view taken on the line 44 of FIGURE 3;

FIGURE 5 is a fragmentary horizontal sectional view taken on the line 55 of FIGURE 3;

FIGURE 6 is a fragmentary vertical sectional view illustrating a detail of construction of the male die;

FIGURE 7 is a perspective upside-down view of the forming ring of the male die; and

FIGURE 8 is a fragmentary perspective view illustrating the corner portion of a completed container.

Referring now to FIGURE 1, a sheet of formable material 10, such as polyolefin, is of fixed dimensions and is firmly grasped around its circumefrential edges by a holding device 20. A female die 30 is disposed beneath the sheet 10 while a male die or plug 40 is disposed above the sheet 10. Prior to the positioning of the sheet as shown in FIGURE 1, the initial step in the manufacturing operation is to heat the sheet of material to its sag point in a separate oven location, and thereafter immediately move it by means of the holder 20 to its position as shown in FIGURE 1, interposed between the male and female dies.

In accordance with the present invention the preliminary forming of the material is done only by the female die 30, by an evacuation process. In order to accomplish this step of the operation the sheet and the female die are moved relative to each other, so that the upper circumferential edge of the female die sealingly engages the undersurface of the sheet 10. Evacuation of the female die 30 causes the central portion of the sheet 10 to assume the position shown in FIGURE 2; and continued evacuation causes the sheet to assume very nearly the form of the interior wall and bottom surfaces of the female die. Thereafter the female die 30 and male die are moved vertically relative to each other, into interengaging relationship as shown in FIGURE 3. After the interengagement of the two dies the vacuum in the female die is removed and pressure is applied, causing the material to be pressure formed upon the face of the male die 40, as indicated in FIGURES 3 and 4.

In accordance with the present invention a significant feature of the illustrated apparatus is that the side and end walls of plug 41 of the male die 40 are exactly parallel to each other. A forming ring 42 is vertically movable on male plug 41 to any selected position (shown in dotted lines at alternate location to accommodate the male die to any desired container height. A bottom member 33 provides the bottom wall of the female die 30, and is vertically adjustable to any desired vertical position to accommodate the vertical height of a particular container to be formed, and may be fastened in any desired position of vertical adjustment, by means not shown.

In accordance with conventional practice the temperature of the sheet of material 10 is carefully controlled prior to its application to the female die 30, and the female die is heated by some suitable means such as the external strip heaters 34 which encircle the side and end walls thereof.

Female die 30 is provided with an air hose 36 which communicates with the underside of movable bottom member 33, and a plurality of air openings 37 are formed in the bottom member 33 for providing vacuum, or pressure, as the case may be, to the interior of the female die. The equipment is automatically controlled, by means not shown, so that the application of vacuum to the interior of the female die occurs after the upper circumferential edge of the female die has engaged, and preliminarily sealed, the undersurface of the work sheet 10. As best seen in FIGURE 2 the upper circumferential edge of the female die 30 is provided with an upstanding portion 38, on the outside of which there is a circumferential shoulder 39. It is the die portion 38 which accomplishes the preliminary sealing action, while as will be subsequently described there is later a final sealing action in which the shoulder 39 is also utilized.

The male mold or die 40 includes as its primary element a plug 41 which is of substantially rectangular block configuration. The plug or block 41 is surrounded by a rectangular (as viewed in the horizontal plane) ring 42, which ring is vertically adjustable up and down to a selected position of adjustment relative to the plug or block 41. The undersurface of the ring 42 is provided with a groove 43 which, in the position of the apparatus as shown in FIGURE 3, effectively interengages the edge 38 and shoulder 39 of the female die 30, not directly, but by grasping the corresponding portion of the sheet 10 therebetween.

It will therefore be seen that the vertical position of the ring 42 relative to the plug 41 of the male mold 40 must conform to the vertical position of the movable bottom member 33 relative to the female mold 30, the positions of both being selected to provide a container having a desired vertical height. Female die 30 rest on top of a floor support 30a while the male die 40 is suspended underneath a ceiling support device 40a. Ring 42 is suspended from the ceiling support 40a by a plurality of ring support devices 44; plug 41 is supported by means of a plurality of plug support devices 46; and the support devices 44 are adjustable so as to vary the relative vertical positions of the ring 42 and the plug 41.

The fully formed container as shown in FIGURES 3 and 4 has a bottom wall 11, end walls 12, and side walls 13; while unused portions 14 of the sheet 10 which lie external to the dies are subsequently cut off and scrapped. The upper circumferential edge of the container has a cross-sectional configuration which is essentially an inverted short-handled dipper. There is horizontal inner shoulder portion 15 corresponding to the short handle of the dipper; a vertical inner flange portion 16 which extends upwardly; a horizontal rim portion 17 which extends outwardly; and finally an outer flange portion 18 which extends vertically downwardly. This configuration of outer flange 18, and the outer portion of rim 17, is achieved by the compression forming of the material between the ring 42 of the male mold and the portion 38 of the female mold. It will thus be seen that the mechanical tolerances of the upper circumferential portion of the container are precisely controlled by the configuration of the two dies, with the result that reliable stacking support of a, superimposed container may be achieved. From the standpoint of the forming operation the manner in which the upper rim of the container is formed is significant in that it provides a positive final seal, whch supersedes or replaces the preliminary seal that was previously referred to.

When the container walls and bottom are pressed upon the exterior surfaces of the male plug 41 there would be a possibility of entrapping air therebetween. For that reason a plurality of exhaust holes 41a, such as shown in FIGURE 6, are spaced throughout the bottom, side and end walls of the male plug. On the side and end walls where vertical ridges 49a are part of the structure of the male plug, the exhaust openings are preferably formed or located in the valleys on each side of such ridges. Complete escape of air from the interior of the container, through the exhaust holes 41a, into the hollow interior of the male plug 41, is therefore assured.

A specific feature of the presently illustrated embodiment of the invention is the provision of vertical ridges on the exterior of the male plug 41, which permits forming vertical grooves on the interior walls of the completed container. As shown in FIGURE 7, forming ring 42 has an inner flange 39 in which interior grooves 39a are formed to receive the ridges 49a, and has exterior ridges 39b which form grooves 16a of the container. The top of flange 39 forms shoulder 15 of the container. The specific advantages of the ridged and grooved container construction are fully described in the above referred to patent.

As previously explained, the work piece 10 is heated in a separate oven before being placed between the two dies of the present invention. When polyolefin material is utilized the pre-heating temperature is approximately 400 degrees F. Female die 30 is heated to a somewhat lower temperature by means of the strip heaters 34. The male plug 41 is kept at a much lower temperature, in the approximate range from degrees to 200 degrees F., with its specific temperature depending upon the specific material being utilized and the size and height of the container being formed. The pipes or ducts 47 and 48 are coupled in series configuration, and temperaturecontrolled water is circulated therethrough for maintaining the temperature of the male plug 41 at a predetermined level. In general, the shallower the container that is being formed the colder the temperature level that is maintained for the male plug; and for deeper containers, the male plug temperature is established at a higher level. In any event the male plug is maintained at a constant temperature, as nearly as possible, which constant temperature is far below the setting temperature for the material, with the result that as soon as the material commences to be formed on' the male plug a cooling action is initiated which-causes the material to start to set.

Female die 30 is provided with a cooling pipe 35 which extends around the external circumference of the die, being located near the upper wall extremities thereof. Pipe .35 is provided with spaced small openings on its upper surface. When the material commences to be formed'on the male plug 41, cooling of the material is initiated, air is forced under pressure into the pipe 35, and is blown upwardly and outwardly onto the under surface of the scrap material 14, with consequent rapid cooling thereof.

Cooling of the material is also initiated on the interior of the female die 30, at the time when the material is pressed against the male plug 41. Female die 30 in one end wall 31 thereof is provided with a relief valve 36a, which is set at a fixed pressure level such as, for example, 40 pounds per square inch. Air pressure is applied via the air hose 36 to the interior of the female die 30, for the purpose of pressing the material onto the male plug 41; the pressure of the source that is connected to air hose 36 is substantially in excess of the pressure level for which the relief valve 36a is set; and the result therefore is that as soon as this control pressure level is reached inside the female die, air continues to flow at a rapid rate from the hose 36 to the openings 37 to the interior of the female die, and to be continuously exhausted from the interior of the female die through the exhaust valve 36a.

Thus the cooling and setting of the material is accomplished by means of the flow of air inside the female die 30, by the relatively cold temperature level of the male plug 41 prior to its being contacted by the much hotter material, and by the continued cooling of male plug 41 via the temperature controlled water flowing inside the ducts 47 and 48. At the same time the air supply to pipe 35 ensures the very rapid cooling of the excess of waste material 14.

It is of basic importance in accordance with the pres ent invention that the upper circumferential edge, or rim portion, of the container is cooled more slowly than the remainder thereof. There are three separate factors which contribute to this slower cooling of the rim portion of the container:

(1) the initial distribution of the material is controlled in such a way that the rim portion of the container is slightly thicker than the side and bottom wall portions;

(2) the compression forming of the rim portion of the container, by its inter-engagement between the male and female dies, results in the material being of higher density in that area;

(3) the compression forming the rim portion of the container results in its having a lesser degree of exposure to the source of the cooling action in the female die, namely the flowing air inside the female die.

It is true that the flow of air inside the female die cools the metal side and end walls of the female die, which in turn have some cooling effect on the rim portion of the container. It is also true, however, that the cooling action of the air flowing inside the female die upon the side and end walls of the container is far more direct, and consequently far more rapid in its effect.

An essential characteristic of the polyolefin or other material used in accordance with the invention is that it contracts during the cooling and setting process. The slower cooling of the rim of the container therefore results in the upper portions of the side and end walls remaining in a slightly expanded condition, at least a few thousandths of an inch, relative to the lower portions of the side and end walls, prior to the material having completed its setting process. The container is then stripped from the mold, before the setting action is completed, and while the upper wall portions are still in this slightly expanded condition.

It is necessary that the forming ring 42 have a tight running fit with the male plug 41 in any position of vertical adjustment of the forming ring. From this requirement it necessarily follows that the side and end walls of the male plug 41 are precisely parallel to each other. Nevertheless, despite this lack of draft on the mold, the novel method of the present invention, of stripping the container from the male plug just beforethe setting process is completed, is successful in forming the containers in accordance with a good standard of quality, and at the high rate of speed required in modern manufacturing facilities.

In the present drawings the relief valve 36a of the female die is shown located above the particular position in which the movable bottom member 33 has been fastened. However, it is in fact preferred to locate the relief valve near the bottom of the female die, in such position that it will always lie beneath the bottom member 33. The advantage of that arrangement is that it prevents any contact between the container material and the intake port of the relief valve, and therefore precludes the possibility of malforming of the container by virtue of the exhaust flow of air out of the relief valve.

Pressure forming on the male plug 41 has at least one advantage which is quite inobvious. This has to do with the adjustability of the tool for different container heights. When a container of low height is being formed there are quite a number of the exhaust holes 41a which lie above the forming ring 42; however, it is not necessary to close off these unused exhaust ports. If, on the other hand, the male plug 41 were being exhausted by evacuation of its interior, any unused opening communicating between the interior and exterior of the male plug would have to be closed off, and this requirement would present a very difficult problem relative to the adjustable use of the tool.

The method and apparatus of the present invention can be used on straight-walled containers, as well as the ridged wall structure as presently illustrated. An advantage of the ridged wall construction is, however, that a lesser amount of material is required to achieve the same degree of structural support for stacked or superimposed containers.

It will be seen that hose section 48 is carried in the forming ring 42 and movable therewith, and that the hose sections 47 and 48 are coupled together by a flexible intervening section 47a.

The invention has been described in considerable detail in order to comply with the patent laws by providing a full public disclosure of at least one of its forms. However, such detailed description is not intended in anyway to limit the broad features or principles of the invention, or the scope of patent monopoly to be granted.

I claim:

1. A method of forming, from thermoplastic material characterized by shrinkage which continues during the cooling and setting process, an integral container having precisely parallel vertical walls comprising the steps of:

selecting a sheet of thermoplastic material;

preheating at least a portion of said sheet of material;

preheating a female die;

heating a male die to a preselected temperature and thereafter maintaining the male die at said temperature;

moving the preheated material and female die relative to one another to bring the material into contact with the periphery of the female die;

vacuum drawing the material into the female die;

lowering the male die into the female die to press the material between the male and female dies about the periphery of the female die to thereby form a container rim of increased thickness and density;

fluid pressure forming the material within the female die about the male die;

delivering cooling fluid to the interior of the female die to cool exposed portions of the material which 1 7 are in contact with the male die, the material in the region of the container rim being protected from the cooling fluid by being compressed between the heated male and the female-dies, the material in the region of the container rim thereby remaining in an expanded and softened condition; and

stripping the thus formed container from the male die and allowing the rim region thereof to set. 2. The method of claim 1 further-comprising the step of: a

rapidly cooling the scrap material about the exterior of the female die after the material has been formed about the male die. 1

References Cited UNITED 1 ROBERT F. WHITE,

STATES PATENTS Primary Examiner.

A. R. NOE, Assistant Examiner. 

1. A METHOD OF FORMING, FROM THERMOPLASTIC MATERIAL CHARACTERIZED BY SHRINKAGE WHICH CONTINUES DURING THE COOLING AND SETTING PROCESS, AN INTEGRAL CONTAINER HAVING PRECISELY PARALLEL VERTICAL WALLS COMPRISING THE STEPS OF: SELECTING A SHEET OF THERMOPLASTIC MATERIAL; PREHEATING AT LEAST A PORTION OF SAID SHEET OF MATERIAL; PREHEATING A FEMALE DIE; HEATING A MALE DIE TO A PRESELECTED TEMPERATURE AND THEREAFTER MAINTAINING THE MALE DIE AT SAID TEMPERATURE; MOVING THE PREHEATED MATERIAL AND FEMALE DIE RELATIVE TO ONE ANOTHER TO BRING THE MATERIAL INTO CONTACT WITH THE PERIPHERY OF THE FEMALE DIE; VACUUM DRAWING THE MATERIAL INTO THE FEMALD DIE; LOWERING THE MALE DIE INTO THE FEMALE DIE TO PRESS THE MATERIAL BETWEEN THE MALE AND FEMALE DIES ABOUT THE PERIPHERY OF THE FEMALE DIE TO THEREBY FORM A CONTAINER RIM OF INCREASED THICKNESS AND DENSITY; FLUID PRESSURE FORMING THE MATERIAL WITHIN THE FEMALE DIE AND THE MALE DIE; DELIVERING COOLING FLUID TO THE INTERIOR OF THE FEMALE DIE TO COOL EXPOSED PORTIONS OF THE MATERIAL WHICH ARE IN CONTACT WITH THE MALE DIE, THE MATERIAL IN THE REGION OF THE CONTAINER RIM BEING PROTECTED FROM THE COOLING FLUID BY BEING COMPRESSED BETWEEN THE HEATED MALE AND THE FEMALE DIES, THE MATERIAL IN THE REGION OF THE CONTAINER RIM THEREBY REMAINING IN AN EXPANDED AND SOFTENED CONDITION; AND STRIPPING THE THUS FORMED CONTAINER FROM THE MALE DIE AND ALLOWING THE RIM REGION THEREOF TO SET. 